Suspension systems for motor vehicles are known which isolate the vehicle load from irregularities in the terrain over which the vehicle travels. A semi-active suspension system, for example, normally includes a spring and a damper connected between the sprung and unsprung portions of the vehicle. Semi-active suspension systems are generally self-contained, and only react to the loads applied to them. In active suspension systems, by contrast, the reactions to the applied loads are positively supplied by electronically controlled hydraulic or pneumatic actuators.
In addition to isolating the sprung portion of the vehicle from the road, it is desirable to stabilize the tendency of the sprung portion of the vehicle to tilt or roll relative to its unsprung portion when accelerating, decelerating or cornering at relatively high rates. Therefore, suspension systems have been proposed that attempt to maintain the vehicle in an essentially level position, regardless of the source of the force seeking to upset that position. For example, U.S. Pat. No. 4,206,935 to Sheppard et al. discloses a motor vehicle roll control system which includes anti-roll force adjustment means whereby the action of anti-roll bars can be modified within predetermined limits.